In recent years, environmental requirements have requested us to purify, with catalysts, exhaust gas discharged from a general-purpose engine mounted on a working machine. However, in many cases, an exhaust pipe passage in a small-sized general-purpose engine is smaller in length than an exhaust pipe passage in a vehicle, such as a four-wheeled automotive vehicle or a motorcycle. Thus, a catalyst layer has to be provided in the interior of a small-sized muffler. Examples of a muffler for a general-purpose engine are know from Japanese Patent Application Laid-open Publication No. 2004-92462 (hereinafter referred to as “Patent Literature 1”) disclosing a construction including a catalyst layer and from Japanese Patent No. 2989791 (hereinafter referred to as “Patent Literature 2”) disclosing a construction including no catalyst layer.
In the muffler disclosed in Patent Literature 1, a partition plate is interposed between two divided muffler body members to define two expansion chambers in the interior of the muffler body, and an exhaust gas purifier is provided in an exhaust gas flow passage between the two expansion chambers. Flanges are formed on divided surfaces of the muffler body, and the above-mentioned partition plate is fixed to the individual flanges by caulking, brazing, screwing or otherwise. The exhaust gas purifier is coated with catalysts.
Further, in the muffler disclosed in Patent Literature 2, a partition plate is interposed between two divided muffler body members to define two expansion chambers in the interior of the muffler body. Flanges are formed on divided surfaces of the muffler body, and the above-mentioned partition plate is sandwiched between and integrally fixed to the individual flanges with one of the flanges folded back onto the other flange.
However, in order to enhance efficiency of purification by the catalysts, it is necessary to set an exhaust pipe length within the muffler in such a manner that temperature of exhaust gas passing through the catalyst layer falls in an active temperature range of the catalysts. Further, in order to enhance muffling performance of the muffler, it is necessary to set optimal capacity of the plurality of expansion chambers as well as the exhaust pipe length.
Namely, an appropriate length of the exhaust pipe and capacity of each of the plurality of expansion chambers within the muffler have to be set separately for each of exhaust characteristics of various general-purpose engines. For that purpose, there arises a need to change sizes (dimensions) of individual component parts of a muffler for each of exhaust characteristics of various general-purpose engines. Therefore, it is preferable to enhance a degree of dimensioning design freedom and at the same time secure sufficient quality of the muffler.